[PATCH 2 of 3] setup: restrict TurboGears2 version to 2.3.x

[Thomas De Schampheleire]

# HG changeset patch
# User Thomas De Schampheleire <thomas.de_schampheleire at nokia.com>
# Date 1554142001 -7200
#      Mon Apr 01 20:06:41 2019 +0200
# Branch stable
# Node ID 953047e8c88a9c5ccaa4ddc1bb417622de37f01f
# Parent  2b8563d0432ca1359f5ba5dab73af0b42a1743c0
setup: restrict TurboGears2 version to 2.3.x

In TurboGears2 2.3.12, the latest version in the 2.3.x range, the WebOb
dependency requirement is [1]
    WebOb >= 1.2, < 1.8.0

In TurboGears2 2.4.0 (which is in pre-release state at the time of this
commit), this becomes [2]:
    WebOb >= 1.8.0, < 1.10.0

In the Kallithea dependency list, we have matched our WebOb version
requirements to that of TurboGears2 and use:
    WebOb >= 1.7, < 1.8

while our TurboGears2 requirement was liberal and accepted anything in the
2.x range:
    TurboGears2 >= 2.3.10, < 3

To avoid new Kallithea installations failing with conflicting WebOb version
requirements after TurboGears2 2.4.0 is released, restrict the version of
TurboGears2 to 2.3.x on the stable branch.

For the default branch, the update to TurboGears2 2.4.0 can be considered
once it's released.

[1] https://github.com/TurboGears/tg2/blob/tg2.3.12/setup.py#L54
[2] https://github.com/TurboGears/tg2/blob/ed89788c3f5dab5a182a938543c9ee4ec14dd7ef/setup.py#L41

diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -40,7 +40,7 @@ requirements = [
     "waitress >= 0.8.8, < 1.2",
     "WebOb >= 1.7, < 1.8", # turbogears2 2.3.12 requires WebOb<1.8.0
     "backlash >= 0.1.2, < 1",
-    "TurboGears2 >= 2.3.10, < 3",
+    "TurboGears2 >= 2.3.10, < 2.4",
     "tgext.routes >= 0.2.0, < 1",
     "Beaker >= 1.7.0, < 2",
     "WebHelpers >= 1.3, < 1.4",